build: only export PAM interface symbols.
build: rename configure.in for compatibility with new autoconf/automake.
build: do not search for a target.

This is not a compiler, so it should not have a target.
build: remove an outdated reference to INCLUDE in favour of AM_CFLAGS.
Merge pull request #1 from Flameeyes/master

A few build system fixes

Tested as working on Debian wheezy.